Bryan hasn't done a full review, but based on the ISO chart crops, it looks decent. It's softer wide open, but it's 2.8, instead of 3.5. Stopping down to f/4 they both look pretty sharp.

I have no idea how the AF on this lens compares to other Sigmas. I know many of their lenses are known to have focus issues, but if you're using it for Macro, then Sigma's auto-focus issues may not be a concern, as you typically manual focus and use a large F. If you plan to double this lens as a general telephoto / portrait lens you may want to search the web for information about the AF. In terms of sharpness it looks fine.